The invention relates to a valve for controlling fluids. EP 0 477 400 has disclosed a valve of this kind. In this instance, the actuation piston of the valve member is disposed so that it can move in a sealed fashion in a smaller diameter part of a stepped bore, whereas a larger diameter piston, which is moved by a piezoelectric actuator, is disposed in a larger diameter part of the stepped bore. A hydraulic coupling chamber is mounted between the two pistons in such a way that when the larger piston is moved by the piezoelectric actuator for a particular distance, the actuating piston of the valve member is moved for a distance that is enlarged by the translation ratio of the stepped bore diameter.
With valves of this kind, there is a problem in that length changes occur in the piezoelectric actuator, in the valve member, or in the valve housing, as well as in the hydraulic column of the coupling chamber, and these changes must be compensated for. Since the piezoelectric actuator produces a pressure to open the valve in the coupling chamber, this pressure also leads to a loss in the coupling chamber fluid. In order to prevent an evacuation of the coupling chamber, a refilling is necessary. The prior art mentioned at the beginning has disclosed the execution of a tolerance compensation by means of a predetermined leakage. This has the disadvantage that a continuous, open connection is provided in both possible flow directions between the coupling chamber and e.g. a reservoir, because of which the resulting flexibility of the hydraulic chamber negatively influences the functional behavior of the piezoelectric actuator. The known device is embodied so that the hydraulic fluid is hermetically enclosed in the housing. In particular, a consequently enlarged volume leads to a compressibility that reduces the transmission rigidity of the hydraulic column formed by the coupling chamber.